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When you fly to the west coast, you usually pass over the Sierra Nevada mountain range. On a clear day you’ll notice the surrounding forests are irregular; they’ve been “checkerboarded.” Millions of acres have been logged and ”clearcut.” While problematic on many levels, clearcutting imperils the drinking water for 45 million Americans.

Clearcutting is a logging technique where all trees in a given area are cut down. The valuable timber is hauled away and the residue, the “slash pile,” is burned. Then the ground is scraped and sprayed with herbicides to suppress native vegetation. The area is replanted with one species, typically pine. In recent years, this process has been rebranded as “even-age” timber management.

In California, clearcutting is only permitted on private land and usually occurs on property owned by Sierra Pacific Industries – the largest private landowner in the state holding over 1.7 million acres. Since 1990 Sierra Pacific has received permission from the California Forestry Board to clearcut over a quarter million acres.

In 2000, the California legislature debated a bill that would have banned all clearcutting because of concerns about its environmental impact. Democratic Governor Gray Davis killed the law by declaring he would only sign legislation “that was the result of compromise between environmentalists and loggers.” (Sierra Pacific made significant contributions to Davis’ campaign and on July 13, 1999, hosted a fundraiser that raised $129,000 for the Governor.)

Clearcutting has two major consequences. First, it impacts biodiversity. Replacing native trees and plants with a solitary species, pine, may simplify logging but it disrupts the habitat for plants and animals. Clearcutting fractures the fragile forest ecology causing species to migrate and, in some cases, disappear. And, wherever there is clearcutting there are roads for logging trucks; these roads also impact the environment directly by the introduction of polluting vehicles or indirectly by increasing the number of landslides.

Second, clearcutting has a savage impact on water resources. 60 percent of California’s water supply comes from watersheds in the Sierra Nevada – 15 percent comes from the Colorado River and the remaining 25 percent from groundwater. The logging practices of Sierra Pacific have three impacts.

The initial clearing process leaves the Sierra Nevada topsoil exposed and vulnerable. Winter rains often carry the best soil away, clogging streams and damaging habitat far away from the logging site. That’s the problem at Battle Creek a stream that descends from Mount Lassen in California’s Shasta County. The US Bureau of Reclamation is overseeing a $128 million project to revive the Battle Creek Salmon population; five dams are being removed and four others modified so steelhead and winter- and spring-run salmon can return to their spawning habitat. Tragically that same habitat is threatened by erosion resulting from upstream Sierra Pacific clearcutting, authorized by the California Department of Forestry. California doesn’t require loggers to monitor water quality and the agency charged with overseeing fish habitat, California Department of Fish and Game, has been decimated by budget cuts.

The second impact of clearcutting is alteration of the rate of rainwater absorption. In a natural forest, native tree root systems trap and filter rainwater; as a result water percolates slowly through the soil, gradually recharging streams and aquifers over California’s dry months. In “even-age” forests, this process is altered and water is primarily distributed when it’s not needed. In the summer there is less stream water and this negatively affects fish habitat as well as plants and animals on adjacent properties.

The third impact is from the introduction of herbicides. Each year an average of 200,000 pounds of herbicides are used to domesticate California private forests. Until recently, the most commonly used herbicide was Altrazine. In 2004, the European Union banned Altrazine “because of its persistent groundwater contamination.” US researchers are alarmed by Altrazine’s effects as an endocrine disruptor and its epidemiological connection to low male sperm count. (Health problems from aerial herbicide spraying have been reported in Triangle Lake, Oregon where most residents have tested positive for atrazine in their urine.) Recently, Altrazine has been replaced by Roundup, the most widely used US herbicide. The European Union classed Glyphosate, Roundup's main ingredient, as "dangerous for the environment" and "toxic for aquatic organisms".

In 2006, the Union of Concerned Scientists reported on Global Warming and California’s Water Supply: “By the end of the century, if global warming emissions continue unabated, statewide annual average temperatures are expected to rise into the higher warming range (8-10.5°f). This temperature rise will lead to more precipitation falling as rain instead of snow, and the snow that does fall will melt earlier, thus decreasing the spring snowpack in the Sierra Nevada by as much as 90 percent… spring stream flow could decline up to 30 percent.”

There are many signs that California’s water supply is imperiled by global climate change. Clearcutting increases the probability that the Sierra Nevada watershed will be furthered diminished or rendered unfit for consumption. It’s time for Governor Brown and the Legislature to ban clearcutting in all circumstances.

Bob Burnett is a Berkeley writer. He can be reached at bburnett@sonic.net